This invention relates to bearing support means and, more particularly, to bearing support means for variable pitch fan blades associated with gas turbine engines.
Power plants recently developed for large aircraft have included gas turbine engines wherein a power turbine associated with the core engine drives a large diameter fan which provides propulsive thrust for the aircraft. While in the past such fans have generally utilized fan blades having a fixed-pitch, more recently fan-type gas turbine engines have been provided with variable pitch fan blades to increase the operating efficiency of the engine over the entire range of the operating cycle.
In fan-type gas turbine engines, individual fan blades are secured to a disc attached to a shaft driven by a powered turbine such that both the disc and the fan blades rotate at high angular velocity about an axis comprising the centerline of the engine. In addition to the aforedescribed rotation, variable pitch fan blades are each rotatable about their own centerline to accommodate adjustments in blade pitch. Bearing assemblies and bearing seats used to support the fan blades for this latter rotation must be designed to function appropriately under high radial loads imposed by centrifugal forces associated with rotation about the engine centerline and yet must be compatible with weight and cost limitations of the engine.
Currently, it is the practice of those skilled in the art to seat each individual bearing assembly in separate recesses machined into the disc. Since each seat is distinct and remote from each of the other seats, machining of individually recessed seats requires separate machining operations and associated sequential indexing for each seat. Machining of individual recessed seats is additionally complicated by the disc configuration which limits cutting tool access to the bearing seat surface such that conventional straight drive machining equipment cannot be utilized. Rather, right-angle drive boring and facing equipment must be used. As a result of these additional and intricate steps, fabrication of the bearing seats is time consuming and requires expensive machinery, a great degree of operator attention and substantial quality monitoring of each individual recess. The present invention overcomes the aforestated problems associated with the current prior art practice by providing a substantially continuous seating surface which seats a plurality of bearings and which can be fabricated in an economical and relatively expedient manner.